MICHAEL ANTHONY JACKSON is on death row in California. One afternoon 14 years
ago, high on angel dust, he shot and killed a policeman at close range with the
officer鈥檚 own gun. Jackson was convicted of first-degree murder in 1984. But
now his lawyers are trying to overturn this verdict. They argue that persistent
drug use damaged Jackson鈥檚 brain so that he could not have known what he was
doing. And they鈥檝e got brain scans to prove it.
The scans use positron emission tomography (PET), a technique that shows
which regions of the brain are active at any one time. Jackson鈥檚 lawyers say the
frontal lobe of his brain is abnormally inactive. Since this part of the brain
is believed to control judgment, the lawyers argue that Jackson cannot take
responsibility for the shooting, and that his life should be saved. A federal
judge is now reviewing the case, and will announce his decision within
weeks.
Jackson鈥檚 is one of a growing number of murder cases in the US where scans
have been used to mitigate sentences. Defence lawyers are using the scans to
argue that their clients are suffering from behavioural disturbances, such as a
lack of judgment or inadequate sexual restraint. The number of trials is
unknown, but they have become commonplace in several states including
California, Florida and Texas.
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Courtroom prop
Scans are particularly popular in the 鈥減enalty鈥� phase of American murder
trials, when a jury has to decide whether the person they have just convicted
should have a life sentence or die for the crime. Some jurors have admitted that
brain scans helped them to decide against the death penalty.
Criminal cases like these are highly emotive, but scans are increasingly
popular in civil liability cases as well, where they may make an even bigger
mark. 鈥淭he huge sums of money that are at stake are greater than most people
think,鈥� says Alan Waxman, a radiologist at Cedars Sinai Medical Center in Los
Angeles. Several settlements have exceeded a million dollars.
Scans have served as evidence in claims against manufacturers whose
products鈥攕uch as breast implants鈥攁re alleged to have caused people
neurological problems.
Not surprisingly, some neuroscientists are alarmed: science, they say, is
being abused by the courts. PET scans simply reveal which parts of the brain are
active at the time of the scan, by providing a snapshot of the level of glucose
being used in different parts of the person鈥檚 brain. The more glucose used, the
greater the activity in that area.
But whether a scan says anything about a person鈥檚 behaviour鈥攅ven at
that moment, let alone at some time in the distant past鈥攊s highly
contentious, says Waxman. 鈥淲e鈥檙e simply not in a position at this time to use
functional imaging to explain behaviour,鈥� he says. Nor can a scan prove that a
brain has been damaged by toxins.
鈥淚t can be very damaging evidence,鈥� says Tori Levine, a lawyer in Dallas, who
has both won and lost cases for the company Dow Corning over its silicone breast
implants. The implants have been blamed for various nonspecific autoimmune
illnesses as well as behavioural disturbances.
And the computerised images that translate information about glucose use into
鈥渕aps鈥� of the brain can be very compelling. 鈥淭hese are pictures with
electrifying colours,鈥� says Levine. Waxman goes further, arguing that in
generating these images, scientists can use whatever colours they like, in
whatever combination they like. 鈥淭hat can be misleading,鈥� he says.
The debate over what kind of scientific evidence should be admissible in
court came to a head in 1993, when two women sued the drugs company Merrell Dow
in California, claiming that its product Bendectine had caused birth defects.
The women鈥檚 lawyers wanted to use an unpublished scientific report which linked
the drug to birth defects, but in Californian court at that time, only
scientific evidence that had been peer-reviewed was allowed. The issue was
referred to the Supreme Court.
In a lengthy landmark ruling, the Supreme Court established a new federal
standard which allows judges to decide whether scientific evidence is relevant
and reliable enough to be put before juries.
Levine says that judges are reluctant to bar scientific evidence because if
it is later deemed important, the case can be retried. But if the judge lets
irrelevant or unreliable scientific evidence in, it may just be seen as
鈥渉armless error鈥�, she says. Fearing appeal, most judges open the gates wide.
Helen Mayberg, a behavioural neurologist at the University of Texas Health
Science Center in San Antonio, Texas, fears that this approach is turning
science into a courtroom prop. Mayberg has been an expert witness in more than a
dozen trials. 快猫短视频s are still trying to understand the precise links
between brain structures and complex behaviours, she says. While those links
remain uncertain, she argues, 鈥渁ny scan abnormality can be used to show whatever
you want鈥�.
鈥淚f you take a jury and tell them, this area isn鈥檛 working right and it鈥檚 the
judgment centre, they just might believe you,鈥� says Mayberg. 鈥淏ut if we don鈥檛
know where judgment is in the brain, then how does the scan explain why the guy
ran over to the police car, ripped the gun from its safety [clasps], and cocked
it? Does it explain why, when the cop let down his guard, Jackson shot him?鈥�
Mayberg says that defence lawyers never claim to be explaining the behaviour in
full; they merely suggest that brain abnormalities might have had something to
do with it. 鈥淏ut in the criminal court, uncertainty sides with the accused,鈥� she
says.
She is not alone in her concern. The Society of Nuclear Medicine, an
international body whose members produce and interpret scans, was so uneasy
about their growing misuse that in 1994 it set up a committee to establish
guidelines on their use. Chaired by Mayberg, the committee published its advice
in the Journal of Nuclear Medicine last July.
The guidelines exhort scientists not to draw conclusions from brain scans
that they cannot support. Scans that have not been published in the literature
or repeated by others should never be presented as 鈥渙bjective evidence鈥� of
behavioural abnormality, say the guidelines. Nor should scientists make claims
about scans when they are not backed up by wider evidence from large-scale
studies that a particular scan pattern reliably identifies a particular problem.
Brain scans for court use should come with disclaimers about what they can
show.
But guidelines are only guidelines, and scientists are free to interpret them
as they see fit. Monte Buchsbaum, director of the PET Laboratory at the Mount
Sinai Medical Center in New York, believes that scans can provide important
objective information in court. 鈥淭hey can鈥檛 measure the ability to tell right
from wrong in centimetres of blood flow per minute,鈥� he says, 鈥渂ut they can tell
you a lot about human skills like planning and judgment.鈥� He has been an expert
defence witness some ten times.
It is expert testimony from Buchsbaum鈥檚 former lab at the University of
California, Irvine, that might save Jackson鈥檚 life. Buchsbaum鈥檚 successor at the
Irvine lab, Joseph Wu, did Jackson鈥檚 PET scan and interpreted the findings for
the defence.
He told the judge that he found evidence of abnormally low activity in
Jackson鈥檚 frontal lobe. This was consistent, he testified, with what his lab had
found with other people who abused angel dust. The drug, phencyclidine or PCP,
was developed as an anaesthetic, but doctors stopped using it because of its
severe reactions. Long-term use can cause memory loss, speech problems and
depression. The Irvine team believes that the drug also impairs judgment.
鈥淚 limited my testimony to whether the scan was similar or dissimilar to
those of other chronic PCP users,鈥� says Wu. 鈥淎nd I think we can make the
inference that it鈥檚 compatible.鈥� The findings suggest that Jackson鈥檚 judgment
might have been impaired, says Wu.
Personality change
Mayberg, who was called as expert witness for the prosecution, testified that
almost nothing is known about the pattern that chronic PCP use might produce on
a PET scan. The Irvine group had published only a two-page abstract of their
work on PCP, and this was a study of only seven chronic users. Could Jackson be
considered a chronic user and have his scan compared with those of chronic
users, Mayberg asks, even though he had not used the drug for more than a
decade? She also says that a brain scan on a man sentenced to death might be
abnormal for other reasons, such as the stress of his situation.
Nevertheless, scans such as those Wu does are having an increasing impact, in
civil cases as well as criminal cases. Many of the Irvine lab鈥檚 clients have
sued insurance companies over invisible ailments such as 鈥渇rontal lobe
syndrome鈥�. Most have been involved in accidents which they say damaged their
concentration or changed their personality. Structural brain scans of these
people using computerised tomography鈥攁 technique which, unlike PET, shows
only the structures of the brain, not its activity鈥攕how nothing amiss. But
Wu鈥檚 PET scans reveal abnormality. This is objective, says Wu. 鈥淵ou can鈥檛 fake
turning off part of your frontal lobe.鈥�
However, PET scans are not as objective as some would claim. As the Society
of Nuclear Medicine鈥檚 committee pointed out, everything from the model of
scanner to a twitch of the head can affect the resulting image, and
interpretations of it also vary.
While scans hold such sway, cases like Jackson鈥檚 will remain wide open. Yet
the concerns of scientists are growing. 鈥淲hen law and science cross, it鈥檚 not
clean,鈥� says Mayberg. 鈥淚n law, they want everything reduced to black and white.
In science we live comfortably in grey.鈥�